title: Inflammation-dependent secretion and splicing of IL-32{gamma} in rheumatoid arthritis.
abstract: Different splice variants of the proinflammatory cytokine IL-32 are found in various tissues; their putative differences in biological function remain unknown. In the present study, we report that IL-32γ is the most active isoform of the cytokine. Splicing to one less active IL-32β appears to be a salvage mechanism to reduce inflammation. Adenoviral overexpression of IL-32γ (AdIL-32γ) resulted in exclusion of the IL-32γ-specific exon in vitro as well as in vivo, primarily leading to expression of IL-32β mRNA and protein. Splicing of the IL-32γ-specific exon was prevented by single-nucleotide mutation, which blocked recognition of the splice site by the spliceosome. Overexpression of splice-resistant IL-32γ in THP1 cells or rheumatoid arthritis (RA) synovial fibroblasts resulted in a greater induction of proinflammatory cytokines such as IL-1β, compared with IL-32β. Intraarticular introduction of IL-32γ in mice resulted in joint inflammation and induction of several mediators associated with joint destruction. In RA synovial fibroblasts, overexpression of primarily IL-32β showed minimal secretion and reduced cytokine production. In contrast, overexpression of splice-resistant IL-32γ in RA synovial fibroblasts exhibited marked secretion of IL-32γ. In RA, we observed increased IL-32γ expression compared with osteoarthritis synovial tissue. Furthermore, expression of TNFα and IL-6 correlated significantly with IL-32γ expression in RA, whereas this was not observed for IL-32β. These data reveal that naturally occurring IL-32γ can be spliced into IL-32β, which is a less potent proinflammatory mediator. Splicing of IL-32γ into IL-32β is a safety switch in controlling the effects of IL-32γ and thereby reduces chronic inflammation.
authors.affiliation: Rheumatology Research and Advanced Therapeutics, Department of Rheumatology, Radboud University Nijmegen Medical Centre, 6500 HB, Nijmegen, The Netherlands.
authors.forename: Bas
authors.initials: B
authors.lastname: Heinhuis
authors.forename: Marije I
authors.initials: MI
authors.lastname: Koenders
authors.forename: Fons A
authors.initials: FA
authors.lastname: van de Loo
authors.forename: Mihai G
authors.initials: MG
authors.lastname: Netea
authors.forename: Wim B
authors.initials: WB
authors.lastname: van den Berg
authors.forename: Leo A B
authors.initials: LA
authors.lastname: Joosten
mesh_terms: D016475:3T3 Cells; D000256:Adenoviridae; D017398:Alternative Splicing / Q000235:genetics / Q000276:immunology*; D000818:Animals; D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D016207:Cytokines / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D005347:Fibroblasts / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D006367:HeLa Cells; D006801:Humans; D007249:Inflammation / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D007378:Interleukins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D020033:Protein Isoforms / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D022821:RNA Splice Sites / Q000235:genetics; D013583:Synovial Membrane / Q000276:immunology* / Q000378:metabolism / Q000473:pathology
chemical_list: D016207:Cytokines; C496971:IL32 protein, human; D007378:Interleukins; D020033:Protein Isoforms; D022821:RNA Splice Sites